The present disclosure relates to an image forming apparatus that conveys a paper sheet and includes an image sensor provided on a conveyance path.
There are various types of image forming apparatuses such as a printer, a multi-functional peripheral, a copy machine, and a facsimile apparatus. These types of image forming apparatuses perform printing on a paper sheet while conveying the paper sheet. Some types of image forming apparatuses perform detection related to a paper sheet being conveyed. There is known one example of a technique related to such detection performed in the process of conveyance as described below.
Specifically, there is a disclosure of an image recording apparatus that, with respect to a recording medium being conveyed in a sub-scanning direction, records an image on the recording medium in a main scanning direction, detects a density on the recording medium on an upstream side beyond a paper sheet tip end position in the sub-scanning direction when a recording head performs recording of a first band of the image with respect to the recording medium, and determines, based on a result of the detection, a width and a position of the recording medium. An infrared sensor is used to detect the density. According to this configuration, before printing of the first band is performed with respect to a paper sheet or by the time when printing of the first band is performed with respect thereto, a density on a recording medium is detected. This is intended to determine a width and a position of the recording medium.
A reading sensor may be provided on a conveyance path. The reading sensor reads a paper sheet being conveyed (a paper sheet with respect to which printing is to be performed). Based on a result of the reading, detection related to the paper sheet is performed. In order to perform accurate detection, preferably, a resolution of an image obtained through the reading does not vary. In order to maintain a constant resolution of an image obtained, it is required that a reading width per line (per dot) be made uniform. To this end, a line reading cycle of the reading sensor may be set using a pulse cycle for causing a paper sheet conveyance motor to rotate. For example, such a reading cycle is set to an integral multiple of a pulse cycle. Thus, regardless of a rotational speed of the motor, upon every given amount of conveyance of a paper sheet, the paper sheet can be read by an amount corresponding thereto.
Meanwhile, in order to improve productivity, a paper sheet conveyance speed may be switched on a conveyance path. For example, there are provided a plurality of motors for causing rotors on the conveyance path to rotate. Further, the motors may be made to vary in rotational speed. In this case, a speed of each of the motors is individually accelerated/decelerated. Due to a difference in acceleration/deceleration pattern between the motors, a conveyance speed at which a paper sheet is conveyed while passing through the reading sensor may fluctuate.
When a reading cycle is set on the basis of a drive pulse of a particular one of the motors, due to a difference in acceleration/deceleration pattern between the motors, there may occur variations in reading width per line. Consequently, in a case where a paper sheet is conveyed by use of a plurality of motors varying in acceleration/deceleration control pattern, there is a problem that a reading width per line (a resolution) cannot be made uniform.
In the above-mentioned known technique, before printing of a first band of an image is performed with respect to a paper sheet or by the time when printing of the first band is performed with respect thereto, a position or the like of a recording medium can be detected. However, no mention is made of a change in paper sheet conveyance speed. Consequently, the above-described problem could not be solved by the known technique thus described.